As climate change accelerates ice melt in the Arctic, polar bears may find caribou and snow geese replacing seals as an important food source, shows a recent study published in the journal PLOS ONE. The research, by Linda Gormezano and Robert Rockwell at the American Museum of Natural History, is based on new computations incorporating caloric energy from terrestrial food sources and indicates that the bears’ extended stays on land may not be as grim as previously suggested.

“Polar bears are opportunists and have been documented consuming various types and combinations of land-based food since the earliest natural history records,” said Rockwell, a research associate in the Museum’s Department of Ornithology who has been studying the Arctic ecology of the Western Hudson Bay for nearly 50 years. “Analysis of polar bear scats and first-hand observations have shown us that subadult polar bears, family groups, and even some adult males are already eating plants and animals during the ice-free period.”

Previous studies have predicted mass polar bear starvation by 2068, when annual ice breakup is expected to separate the bears from their sea-ice hunting grounds for a consecutive 180 days each year–creating ice-free seasons that will last two months longer than those in the 1980s. But those estimates assumed no energetic input from land food sources.

Gormezano and Rockwell computed the energy required to offset any increased starvation and then determined the caloric value of snow geese, their eggs, and caribou that live near the coast of the Western Hudson Bay. They found that there likely are more than enough calories available on land to feed hungry polar bears during the lengthening ice-free seasons.

Although the exact energetic cost for a bear to hunt geese and caribou is uncertain, polar bears in Manitoba have been reported ambushing caribou with the same energetically low-cost techniques they typically use to hunt seals. The similar size of these two prey species means that bears would need to hunt for caribou only as often as they would usually hunt for seals, the researchers say.

“If caribou herds continue to forage near the coast of Western Hudson Bay when bears come to shore earlier each year, they are likely to become a crucial component of the bears’ summertime diet,” Rockwell said.

The eggs of snow geese are another food source for bears, and the energetic cost of obtaining eggs in ground nests is exceedingly low, the researchers say. With adequate food sources available, snow geese are known to endure polar bear egg predation without detrimental effects to the population.

Scientific consensus holds that the rapidly melting circumpolar ice reserves will increasingly prevent polar bears from hunting the seals on which they currently depend. Nevertheless, these observations of one population along the Western Hudson Bay show that bears marooned on land might, where the conditions are right, stave off starvation by turning to alternate food sources.

One of the questions raised by climate change has been whether it could cause more species of animals to interbreed. Two species of flying squirrel have already produced mixed offspring because of climate change, and there have been reports of a hybrid polar bear and grizzly bear cub (known as a grolar bear, or a pizzly).

“Climate change is causing species’ ranges to shift, and that could bring a lot of closely related species into contact,” said Meade Krosby, a research scientist in the University of Washington’s Climate Impacts Group. She is the lead author of a study published July 6 in Nature Climate Change that tallies the potential number of such pairings. Looking across North and South America, it finds that only about 6 percent of closely related species whose ranges do not currently overlap are likely to come into contact by the end of this century. “People have been concerned that climate change would be bringing all these species into contact, and that this could unleash a wave of interbreeding,” Krosby said. “What we found is, not so much.”

A 2010 editorial in the journal Nature suggested that northern species may begin to interbreed and create a so-called “Arctic melting pot,” and even prompted one artist’s rendition of what those new offspring would look like. The idea also worried land managers looking at how to prepare for climate change. At a workshop, land managers told Krosby they worked with very closely related species separated by small distances. What if managers linked the two areas with a wildlife corridor, and as the climate changed the species started to mix?

This study is an attempt to see how much that should be a concern. It looked at 9,577 pairs of closely related species of birds, mammals and amphibians in North and South America. For the 4,796 pairs whose ranges currently do not overlap, computer models show that only 6.4 percent of them will come into contact due to climate change by the year 2100. The most overlap among species occurred in the tropics, and among birds, likely because more species live in the tropics and birds cover wider ranges, Krosby said.

While the study suggests that climate change is unlikely to result in widespread interbreeding, wildlife biologists still need to consider their particular region and animals of interest to best protect specific populations. “Managers still need to look case-by-case at species at a local scale, but at a global scale, the big picture is that it’s probably not going to be a huge problem,” Krosby said.

The study likely overestimates how many species could be at risk of interbreeding because it assumes that all species will be able to access new habitats that become available due to climate change. In fact, natural barriers prevent animals from reaching all potential new habitats, and humans have created new barriers such as highways, farms, and cities that can block migrations to more hospitable places. “The number one strategy for helping biodiversity respond to climate change is to increase connectivity, to link up habitats that have been fragmented by human activity, so species can move, and track climate as it shifts to stay comfortable,” Krosby said. “If people are worried that wildlife corridors and other ways to increase connectivity could bring these species into contact, we’re saying: That’s probably not going to happen, and allowing species to move is far more important.”

Krosby did her doctoral work looking at how historic climate changes affected species in the past, including how the end of the last ice age led to interbreeding among West Coast songbirds. Now she focuses on contemporary climate change, to see how species are responding and how land managers can best protect biodiversity under faster, human-driven changes to Earth’s climate. Co-authors include Joshua Lawler, an associate professor in the UW’s School of Environmental and Forest Sciences; Joshua Tewksbury, a UW professor of biology; postdoctoral researchers Theresa Nogeire and Julie Heinrichs in the School of Environmental and Forest Sciences; and former UW researchers Chad Wilsey, now at the National Audubon Society; Jennifer Duggan, now at California State University Monterey Bay; and Jenny McGuire, now at the Georgia Institute of Technology. The research was funded by the Wilburforce Foundation, the Doris Duke Foundation and the David and Lucile Packard Foundation.

A study undertaken by scientists from the University of Alberta and Environment and Climate Change Canada to understand swimming behavior in polar bears is showing an increase in this behavior related to changes in the amount and location of summer sea ice. Lead author Nicholas Pilfold, now a postdoctoral fellow at San Diego Zoo Global, said “the pattern of long-distance swimming by polar bears in the Beaufort Sea shows the fingerprint of climate change. Swims are occurring more often, in association with sea ice melting faster and moving farther from shore in the summer.”

The study, published in a recent issue of the journal Ecography, was accomplished using satellite-linked telemetry-tracked populations of polar bears in the Beaufort Sea and Hudson Bay. Results of the study show an increase in swimming associated with reduced ice, due to climate change. In 2012, the year in which Arctic sea ice hit a record low, 69 percent of the tracked adult females in the Beaufort Sea swam more than 31 miles (50 kilometers) at least once.

“Recent studies indicate that swimming may be energetically costly to polar bears,” said Nicholas Pilfold. “Given the continued trend of sea ice loss, we recognize that an increased frequency in the need to engage in this behavior may have serious implications for populations of polar bears living around the Arctic Basin.”

Swimming frequency and other movement factors varied between individual bears and showed differences dependent on age, sex, body size and geographic features of the region. Swims occurred more frequently in the Beaufort Sea than in Hudson Bay. Researchers noted that females with young cubs tended to swim less to avoid submersion of youngsters in cold waters, while lone subadults swam as frequently as lone adults. The longest recorded swim in the study was by a subadult female that traveled over 249 miles (400 kilometers) in nine days.